Indoor unit installed in the basement. I didn't like the fact that I was starting a hole in a concrete block without a guide, a drill. I made a hole in the wall with a 4 point torx bit (1" wide) so there is nothing to guide the tool. The drill that was supposed to guide the tool didn't have much of an effect because the hole in the concrete block was larger.The lack of a guide meant the tool would NOT make a round hole, but that's fine because I didn't need the hole anyway.